Technical Abstract:
Soybean rust, incited by the fungal pathogen Phakopsora pachyrhizi, is a serious foliar soybean disease capable of causing major economic yield loss. Specific resistance to P. pachyrhizi is known and single dominant genes have been identified in soybean (Rpp1-4), but these genes have been deemed ineffective to many isolates of P. pachyrhizi. It is therefore essential to search for other sources of stable genetic resistance, particularly those found in Glycine germplasm accessions. Such resistance genes have been identified in the wild perennial relative G. tomentella. Genes involved in rust resistance in other plant species including wheat, barley, rice, and maize have been reported to have homology to receptor-like kinase (RLK) genes. In soybean, several RLK genes have been identified, among which the leucine-rich repeat (LRR) RLKs are believed to be important in plant disease resistance. In this study, we utilized a virus-induced gene silencing (VIGS) approach to evaluate the contribution of three soybean RLK genes (GmRLK1, Gm RLK2, and GmRLK3), which are similar in amino acid sequences, to rust resistance. We employed the novel bean pod mottle virus (BPMV)-based VIGS vector to effectively silence the RLK genes in both soybean and G. tomentella. Recombinant BPMV vectors containing a 300-bp fragment from GmRLK1 and a 258-bp fragment from GmRLK3 were constructed and used to inoculate rust-resistant G. tomentella accessions. Results showed that silencing of G. tomentella homologs of GmRLK genes suppressed resistance to rust. A rating of 1 was scored for the vector control (no lesions), while ratings of either 4 or 5 (moderate or heavy lesion numbers, respectively) were recorded for RLK-silenced accessions. We are currently using the BPMV-VIGS vector to screen additional candidate rust resistance genes in G. tomentella.